“Global climate is projected to continue to change over this century and beyond. ... For the United States, near-term increases of at least 2.5 degrees Fahrenheit (1.4 degrees Celsius) are projected over the next few decades even under significantly reduced future emissions…”

“Many lines of evidence demonstrate that human activities, especially emissions of greenhouse gases, are primarily responsible for observed climate changes in the industrial era. There are no alternative explanations.”

In many ways the report is a direct challenge to President Donald Trump’s dismissal of concern about climate change, and the contention by EPA administrator Scott Pruitt, Secretary of Energy Rick Perry and others in his administrations that the jury is still out on climate change and humans’ responsibility for it.

But it’s not a gauntlet laid down by outside scientists or activists. It’s an assessment of the latest and best climate science from around the world by 13 federal agencies, including NASA, the EPA and even the Department of Defense, along with a host of leading US scientists.

This graphic from the National Oceanic and Atmospheric Administration shows the rapid warming trend of global average temperatures in recent years, including the first half of 2017.

Credit:

NOAA

And while it was prepared largely under the Obama administration, it's not a political document. The report, entitled "U.S. Global Change Research Program Climate Science Special Report," is the latest result of a longstanding process going back to 1990 that's been carried out under presidents of both parties with a specific mandate of reviewing and reporting the latest and best climate science — what we know about climate change and what we don't know. The last report was released in 2014.

Hayhoe says the report brings together that latest science in a way that “presents us with a stark and unyielding picture of the tremendous impacts humans are having on this planet and, moreover, the importance of the decisions that we are making today to reduce and eventually eliminate our carbon emissions.”

The scientific report is working its way through the federal review process and, Hayhoe says, “has passed peer review, public review, agency review by all agencies and departments with relevant expertise, and review by a committee of the US National Academy of Sciences that was specially convened with the sole purpose of reviewing this report.”

In other words, it has passed all the usual tests for scientific integrity.

But this is an unusual time, and what remains uncertain is whether the report now pass the test of an administration that has an unprecedented hostility to climate science and to some degree science itself.

“The final draft is now being reviewed by the administration,” Hayhoe said. “If the report is approved, then it is just a matter of logistics before it is published. However, the administration may choose to not approve it, or to request changes.”

If that happens, she said, “the author team will then have to decide whether they can make [those changes] or not.”

The White House has criticized the Times for its reporting on the draft document, but Press Secretary Sarah Huckabee Sanders says it will “withhold comment on any draft report before its scheduled release date.”

The draft report makes clear the depth and breadth of the evidence for how and why the climate is being disrupted.

“Evidence for a changing climate abounds,” the authors state in the report’s executive summary, “from the top of the atmosphere to the depths of the oceans. Thousands of studies conducted by tens of thousands of scientists around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; disappearing snow cover; shrinking sea ice; rising sea level; and an increase in atmospheric water vapor. Many lines of evidence demonstrate that human activities, especially emissions of greenhouse (heat-trapping) gases, are primarily responsible for recent observed climate changes."

And it states unequivocally that “greater emissions lead to significantly more warming.”

Those heat waves have not yet been linked directly to human-influenced climate change, but they might yet be. The draft report documents recent advances in the ability of scientists to detect a climate change impact on many extreme weather events.

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